This invention relates to a battery using a metal container consisting of a metal case serving as one polar terminal and a metal cover serving as the antipolar terminal, containing battery system elements within. More particularly, the invention relates to the marking process for the battery products.
To date, such marks as trademarks, model numbers, lot numbers for manufacturing, and dates stamped on battery products made of metal containers have been stamped by a convex die 31 designed for those particular marks onto the designated surface of the battery product, referred to as marking surface 32 in FIG. 4(A), using, which caused local plastic deformation of marking surface 32 as shown in FIG. 4(B). This process, however, decreases the reliability of marking since they become unclear due to wearing 31a or chipping 31b after repeated use of the marking convex die 31. Besides, this process is not suitable for finely detailed marks. When producing battery parts such as cases and covers, numbers and characters must be changed according to client's requests as well as different manufacturing dates, and/or lot numbers, which makes process control of this process more complicated and disadvantageous.
As an other process, ink can be used for printing marks on the designated surface of battery products. However, there is a problem that a part or all of the printed mark is likely to disappear during the succeeding manufacturing and transporting processes, since the printed ink is not necessarily permanent.
In Japanese Patent Laid-Open Showa 54-110001/'80 (Patent Publication Showa 62-27521/'87), a new marking process, in which several characters are marked on the surface of electronic components at one time by an irradiating laser beam, is described. As shown in FIG. 5, laser beam 43 generated from laser rod 41 and focused by optical system 42 passes through mask 4 with pattern holes designed for particular marks. In this process, a laser beam irradiates the marking surface simultaneously, however, the energy of laser beams on the marking surface is reduced by the mask since laser beams are irradiated on the marking surface proportionately to the area of pattern holes, resulting in blurred images on the shiny surface of positive and negative terminals of a battery. If the laser power is increased to obtain clearer images, the life of a mask is greatly shortened since a high-power laser beam is also irradiated onto the mask itself. Also, in terms of productivity and cost, this process is unsuitable as a marking process of battery products, in which various types of marking are required, based on the fact that manufacturing of pattern masks requires relatively long working time and high cost.